The control of attention of environmental, experiential, and executive constrains. Preliminary data suggest that species differences corresponding with differences brain complexity exist in the capacity for executive control of attention. Monkeys are relatively susceptible to environmental constraints (i.e., stimulus control) on attention and subsequent behavior. In the present proposal a series of studies are proposed (a) to study the determinants of attention and the within- and between-species differences in the endogenous versus exogenous control of attention; (b) to relate the control of attention to species differences in working memory and executive function; (c) to assess the role of language in attention and executive function in part by determining the degree to which monkeys and chimpanzees without language can attend, plan, and monitor, and in part by examining the improvement in these skills that follow languages training, to identify procedures that promote controlled attention and relational learning in monkeys and chimpanzees; (d) to identify training or practice techniques that improve the endogenous control of attention; and (3) to relate these behavioral data to patterns of brain activity revealed through imaging, stimulation, and biochemical procedures. In all experiments, participants will respond to computer-generated stimuli (pictures, words, forms) by manipulating a joystick or similar response device. Response time, response accuracy, response topography, eye movements and other performance measures will be recorded as a series of variables are eliminated. Species, age, diagnostic category, and other grouping variables (e.g., memory span, attention profile) will also be used in the analyses. It is anticipated that the results of these experiments will elucidate the utility of non-human primate models of attention, and will improve theories of attention as it is manifest across primate species.